Shuqing Sun

Efficient one-pot synthesis of highly photoluminescent alkyl-functionalised silicon nanocrystals

The chemical reduction of micelles formed by mixing silicon tetrachloride and hexyltrichlorosilane in apolar solvent, where hexyltrichlorosilane serves as both reactant and surfactant, yields brightly luminescent silicon nanocrystals, and enables efficient synthesis of alkyl-functionalised silicon quantum dots (SiQDs) in a single step.

Structure and solvent effect on the photostability of indolenine cyanine dyes

Abstract The structure and solvent effect on the photostability of a series of indolenine cyanine dyes have been investigated. It was found that the photostability did not increase with the increase of the central conjugated chain length and/or substituent groups on the heterocyclic ring. Using UV spectra data, we have found that the photostability of indolenine cyanine dyes in solution increased with increase of the E T (30) values of solvents. The rate of singlet oxygen formation, and β values in different solvents sensitized by the dye alone were measured using fluorescence spectra. Absolute photooxidation rate constants ( k r ) are calculated, based on the determined β values and the decay rate of singlet oxygen ( k d ). All these results well agreed with those obtained from UV spectra.

A General Route to Efficient Functionalization of Silicon Quantum Dots for High-Performance Fluorescent Probes†

A general technique for efficient surface modification of silicon nanocrystals is highly desirable for the development of silicon quantum dots (SiQDs) as fluorescent probes for biological applications. Herein, a facile microwave-assisted hydrosilylation process for the preparation of stable SiQDs in a single step is presented. FTIR spectroscopy indicates that molecules with various terminal functionalities, such as alcohol, alkyl groups, and carboxylic acid, are grafted successfully onto the surface of silicon nanocrystals. The dispersibility of such SiQDs is clearly dependent on the terminal functional groups of the grafted molecules. In addition, the as-prepared SiQDs show excellent cell compatibility, photoluminescence properties, and stability, and their use as long-term intracellular fluorescent probes is also demonstrated. It is envisaged that this facile and effective method for the stabilization and functionalization of SiQDs with tailored wetting and chemical properties will enable wide application of SiQDs in a number of areas.

Understanding the photothermal effect of gold nanostars and nanorods for biomedical applications

The plasmon-based photothermal effect of gold nanorod (GNR) has undergone the most systematic investigation for cancer therapy in the biomedical realm. In recent years, gold nanostar (GNS) has come into sight with its attractive ability to transduce electromagnetic radiation into heat. Understanding photothermal conversion efficiency is thus becoming more important for the selection of suitable materials for photothermal therapy. In this article, we investigated systematically the photothermal conversion efficiency and the molar heating rate of GNS and GNR in three groups (S-group, M-group and L-group, representing groups of nanostructures with central extinctions at shorter, medium and longer wavelengths, respectively), to better understand the behaviour of GNS and GNR in the field of photothermal therapy. In the M-group and L-group, the photothermal conversion efficiencies of GNSs and GNRs are similar, while GNSs have a much higher molar heating rate than GNRs. Among all the samples, L-GNS has the highest molar heating rate, because of its large molar extinction coefficient. In addition, the discrete dipole approximation (DDA) was employed to simulate the optical properties of gold nanoparticles with different shapes, and the photothermal properties of GNSs and GNRs were compared experimentally and theoretically. From both the experimental and the theoretical results, M-GNS and L-GNS exhibit higher extinction efficiencies than M-GNR and L-GNR, respectively.

The preparation, characterization of amorphous Cu–TCNQ film with a low degree of charge-transfer (DCT) and its electric switching properties

Abstract Two sorts of Cu–TCNQ films were prepared and characterized. One kind of film is amorphous, exhibiting novel electrical switching effects. The device configuration is a sandwich structure, typically, Al/amorphous Cu–TCNQ thin film/Cu. Films are grown on a Cu substrate by immersion in saturated malononitrile solutions of TCNQ (7,7,8,8-tetracyanoquinodimethane) at 50∼80 °C. The degree of charge transfer (DCT) in this film is estimated at 0.41 according to the position of the IR absorption line of the CN vibration. The current–voltage ( I – V ) characteristics reveal an abrupt decrease of the impedance from 2.4 KΩ to 6Ω (for a typical sample) at a field strength about 4×10 3 V cm −1 for a 1 μm thick film. The low impedance memory state can be erased by the application of large current in either direction. Moreover, the device switches to the low impedance state again when the field strength across the film is decreased below 2×10 4 V cm −1 . The device is stable over a long period of time and has a life time of roughly 50 switching cycles. A possible switching mechanism is proposed.

Raman-encoded microbeads for spectral multiplexing with SERS detection

Simultaneous detection of multiple molecular targets can greatly facilitate early diagnosis and drug discovery. Encoding micron-sized beads with optically active tags is one of the most popular methods to achieve multiplexing. Noble metal nanoparticle labels for optical detection by surface-enhanced Raman spectroscopy (SERS) exhibit narrow bandwidths, high photostability and intense Raman signals. In this study, we demonstrate the feasibility of spectral multiplexing by SERS using micron-sized polystyrene (PS) beads loaded with SERS-active nanoparticles. The silica-encapsulated SERS nanotags comprise gold nanocrystals with a self-assembled monolayer (SAM) of aromatic thiols as Raman reporter molecules for spectral identification. SERS microspectroscopic images of single Raman-encoded PS microbeads indicate the homogeneous spatial distribution of the SERS-active nanoparticles on the surface of the beads. By using up to five different Raman reporters, 31 spectrally distinct micron-sized beads were encoded and characterized spectroscopically at the single-bead level.

Improved Surface Enhanced Raman Scattering for Nanostructured Silver on Porous Silicon for Ultrasensitive Determination of 2,4,6-Trinitrotoluene

Label-free and low-cost surface-enhanced Raman scattering-active substrates of silver nanostructures on porous silicon have been synthesized. The morphology and spectroscopic properties were investigated as a function of concentration and immersion time. The enhancement factor of optimized silver-porous silicon substrate was estimated to be 2.18 × 108 by the use of p-thiocresol as a Raman probe. The optimized substrate was used to determine 50 pg of 2,4,6-trinitrotoluene. These results demonstrate that the prepared silver-porous silicon substrates are promising for the ultra-sensitive determination of organic molecules.

Microfluidic synthesis of QD-encoded PEGDA microspheres for suspension assay

Uniform and size-controllable QD-encoded poly(ethylene glycol) diacrylate (PEGDA) microbeads were produced using a microfluidic device followed by in situ photopolymerization. An S-shaped and gradually widening channel was designed to allow optimized UV exposure for photopolymerization and to prevent coalescence. The as-obtained PEGDA microbeads exhibited well-defined sphericity and excellent monodispersity with a coefficient of variation (CV) below 5%. The size varied from 7 μm to 120 μm and can be selectively achieved by simply adjusting the experimental parameters. The fluorescence performance of the QDs was well preserved without significant peak broadening or distortion. Seven barcode libraries were realized with bright fluorescence and distinguishing coding signals which could be conveniently decoded by a flow cytometer. Furthermore, a very facile strategy to conjugate biomolecules on the bead surfaces was developed using polydopamine (PDA). A sandwich immunoassay of rabbit IgG was performed and the applicability of the QD-encoded microbeads for suspension assay was demonstrated.

Dopamine coating as a general and facile route to biofunctionalization of superparamagnetic Fe3O4 nanoparticles for magnetic separation of proteins

A facile approach to prepare water-dispersible super-paramagnetic iron oxide nanoparticles (MNPs) is reported. The homogeneous MNPs prepared in organic phase are functionalized with an aqueous solution of dopamine at room temperature. The obtained dopamine modified MNPs (MNP-DA) exhibiting excellent super-paramagnetic property can bind various molecules, including NTA and proteins under mild conditions. To demonstrate the feasibility for biological application, the MNP-DA was used for rapid and efficient magnetic separation of bovine albumin (BSA) carrying fluorescent Au nanoclusters from fluorescein. Furthermore, the MNP-DA was functionalized with Nα,Nα-bis (carboxy methyl)-L-lysine hydrate (NTA) to reversibly immobilize and release histidine-tagged proteins. The present study demonstrates a general and facile route to the efficient modification of magnetic nanoparticles with various functional materials and paves the way for a wide range of biomedical applications of MNPs.

Preparation and photolithography of self-assembled monolayers of 10-mercaptodecanylphosphonic acid on glass mediated by zirconium for protein patterning.

Self-assembled monolayers (SAMs) formed by adsorption of octadecylphosphonic acid (ODPA) on zirconium mediated glass substrates were prepared. In this sandwich structure, Zr(4+) was used as a bi-linker to bind phosphonic acid head group in ODPA to glass substrates. The contact angle of the as-prepared SAMs was measured to be around 104°. X-ray photoelectron spectroscopy (XPS) characterization indicated the modification of Zr(4+) on glass substrates was critical for the formation of reasonably dense, well-ordered SAMs similar in quality to those typically formed on other metal oxide surfaces. Bifunctional molecule, 10-mercaptodecanylphosphonic acid (MDPA), bearing thiol terminal groups for various chemical reactions, was synthesized and formed SAMs on glass using the same approach, which allowed us to control the surface chemistry and functionality through photooxidation of the thiol terminal group. Photopatterning of proteins was performed first by exposing the SAMs to UV light through a mask, followed by protein immobilization to the masked regions through a heterobifunctional linker, while the exposed areas prohibit nonspecific protein absorption. The present strategy, which combined the SAMs assembly and photolithography, offered a facile approach for the fabrication of biomolecule patterning and could be applied to construction of biochips and other applications.